1. Field of the Invention
The present invention relates to the field of digital message transmission and more specifically transmitting message packets over a cellular telephone network.
2. Description of Related Art
In a time division multiple access (TDMA) radio communication system, a base unit controls communication with mobile units within its cell. Each mobile unit is assigned a time slot within a TDMA frame in which to communicate with the base unit.
When the base unit is communicating with one mobile unit, the other mobile units wait idle until there it is their turn to send or receive messages. As more mobile units are added, and/or the message traffic increases, the idle time becomes longer.
Large volume message transmission becomes very costly, slow and complex when the system is driven by a `master` controller, such as a cellular base station, which organizes the mobile units under its control.
In addition to complexity and speed, a centrally controlled communication system is more prone to errors. If an error occurs during communication between the base and mobile unit, there is little or no redundant communicating units. Also, since the base unit controls when communications occur, a timing error by the base may cause many problems with the transmissions of the mobile units.
Cellular radio transmissions tend to be a problem in areas, such as cities, having high rise buildings. The buildings tend to block radio transmissions and cause `shadowing`. A mobile unit communicating with base unit signals has to contend with these shadowing effects. As the mobile unit moves into an area which experiences shadowing, the received signal is attenuated, causing interference and may reduce the signal quality to a degree that the message may not be received at all.
One method of combating shadowing is to position repeaters having antennae dispersed around an area in which radio communication is desired. Antenna rental space has become increasingly more costly causing this method to become increasingly unattractive. Coupling this problem with an increased demand for information transmission has resulted in a need for a method of transmitting information which is simple and inexpensive.
Currently there is a need for a system of radio transmission capable of transmitting an increased volume of information which is simple, inexpensive, and more fault tolerant and efficient than conventional systems.